01 - Preheat your grill to medium-high heat, approximately 400°F.
02 - Wash and scrub the potatoes thoroughly. Place each potato between two wooden spoons or chopsticks to act as a cutting guide. Slice crosswise at 1/8-inch intervals, cutting nearly to the bottom without slicing all the way through.
03 - In a small mixing bowl, combine the melted butter, minced garlic, chopped parsley, thyme leaves, kosher salt, and black pepper. Stir until well blended.
04 - Brush the garlic herb butter generously over each potato, taking care to work the mixture between the slices for even flavor distribution.
05 - Loosely wrap each potato in a double layer of aluminum foil, leaving the top slightly open to allow some crisping during cooking.
06 - Place the foil-wrapped potatoes directly on the grill, cover, and cook for 35 to 40 minutes. Brush occasionally with additional garlic herb butter. Remove the foil for the final 5 to 10 minutes to achieve a crisp, golden exterior.
07 - Transfer the potatoes to a serving platter. Sprinkle with grated Parmesan cheese and chopped chives. Serve immediately while hot.